Gas turbine engines generally include a turbine section downstream of a combustion section that is rotatable with a compressor section to rotate and operate the gas turbine engine to generate power, such as propulsive thrust. General gas turbine engine design criteria often include conflicting criteria that must be balanced or compromised, including increasing fuel efficiency, operational efficiency, and/or power output while maintaining or reducing weight, part count, and/or packaging (i.e. axial and/or radial dimensions of the engine).
Conventional three spool gas turbine engines generally include a turbine section defining a high pressure turbine in serial flow arrangement with an intermediate pressure turbine and a low pressure turbine. However, known three-spool engines include a plurality of turbine frames to accommodate the various bearing assemblies supporting the three spools. Additionally, known three spool gas turbine engines that include interdigitated turbines are generally limited in a quantity of stages that may be interdigitated, due at least in part overhung masses. The combination of a plurality of turbine frames to support a three spool bearing configuration (e.g., the increased axial length and weight to the engine) plus limits on turbine interdigitation due to overhung masses therefore significantly limit actual and potential applications of interdigitated turbine sections.
Therefore, there is a need for structures that may enable further interdigitation of turbines in a turbine section. Additionally, there is a need for a turbine frame that may reduce axial length and weight to an engine.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
The present disclosure is directed to a gas turbine engine defining a radial direction, a circumferential direction, an axial centerline along a longitudinal direction. The gas turbine engine defines an upstream end and a downstream end along the longitudinal direction and includes a turbine frame defined around the axial centerline. The turbine frame includes a first bearing surface, a second bearing surface, and a third bearing surface. The first bearing surface corresponds to a first turbine rotor, the second bearing surface corresponds to a second turbine rotor, and the third bearing surface corresponds to a third turbine rotor, and each turbine rotor is independently rotatable.
In one embodiment, one or more of the bearing surfaces each define an outer bearing race.
In various embodiments, the turbine frame defines a first platform to which the first bearing surface is coupled. In one embodiment, the turbine frame defines a second platform, to which the second bearing surface and the third bearing surface are each coupled. In another embodiment, the second platform is defined inward along the radial direction of the first platform. In still another embodiment, the first platform and/or the second platform defines a sleeve fitted to the turbine frame onto which a bearing assembly is coupled.
In still various embodiments, the first turbine rotor defines a low speed turbine. In one embodiment, the second turbine rotor and the third turbine rotor each define an intermediate speed turbine and a high speed turbine, respectively. In another embodiment, each turbine rotor defines a bearing assembly disposed between each respective bearing surface and each turbine rotor. In still another embodiment each bearing assembly defines a roller bearing, a ball bearing, a journal bearing, or combinations thereof.
In various embodiments, the turbine frame further includes a vane disposed within the core flowpath of the gas turbine engine. The vane includes a surface defining an airfoil. In one embodiment, the engine further includes an outer turbine casing disposed around the turbine frame. The turbine frame further includes a spoke extended generally along the radial direction from outward of the outer turbine casing, and coupled thereto, through one or more of the vanes of the turbine frame. In one embodiment, the turbine frame includes three or more spokes. In another embodiment, the turbine frame further includes a first bearing housing disposed inward of the vane along the radial direction. In still another embodiment, the spoke is coupled to the first bearing housing inward of the core flowpath of the engine. In yet another embodiment, the turbine frame further includes a second bearing housing disposed inward of the first bearing housing along the radial direction, and the second bearing housing is coupled to the first bearing housing. In still yet another embodiment, a first platform is coupled to the first bearing housing and a second platform is coupled to the second bearing housing. The first bearing surface is coupled to the first platform, and the second bearing surface and the third bearing surface are each coupled to the second platform.
In still various embodiments, the engine further includes a first turbine rotor defining a low speed turbine rotor. The first turbine rotor includes a plurality of connecting airfoils coupled to a rotor hub and the rotor hub coupled to a low pressure shaft. The plurality of connecting airfoils are coupled to an outer shroud and a plurality of outer shroud airfoils extend inward along the radial direction. A first stage of the plurality of outer shroud airfoils further includes an arm extended generally inward along the radial direction. The arm is coupled to an axially extended hub, in which a bearing assembly is disposed between the axially extended hub and the first bearing surface of the turbine frame. In one embodiment, the engine further includes a second turbine rotor defining an intermediate speed turbine rotor in which the second turbine rotor disposed upstream of the connecting airfoils of the first turbine rotor along the longitudinal direction. The second turbine rotor includes a bearing assembly disposed between the second turbine rotor and the second bearing surface. The engine further includes a third turbine rotor defining a high speed turbine rotor upstream of the turbine frame along the longitudinal direction in which the third turbine rotor includes a bearing assembly disposed between the third turbine rotor and the third bearing surface.
Another aspect of the present disclosure is directed to a method of operating a gas turbine engine with an interdigitated turbine section. The engine includes a fan rotor, an intermediate pressure compressor, a high pressure compressor, a combustion section, and a turbine section in serial flow arrangement. The turbine section includes, in serial flow arrangement, a high speed turbine rotor, a turbine frame, a first stage of a plurality of outer shroud airfoils of a low speed turbine rotor, an intermediate speed turbine rotor, and one or more additional stages of the low speed turbine rotor, the low speed turbine rotor coupled to the fan rotor via a low pressure shaft, the intermediate speed turbine rotor coupled to the intermediate pressure compressor via an intermediate pressure shaft, and the high speed turbine rotor coupled to the high pressure compressor via a high pressure shaft. The method includes rotating the high speed turbine rotor in a first direction or a second direction along the circumferential direction; rotating the low speed turbine rotor in the first direction along the circumferential direction; and rotating the intermediate speed turbine rotor in a second direction opposite of the first direction.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.